Hybrid vehicles are known that run using engines and motors as power sources. In hybrid vehicles, a regenerative brake can be used that activates a motor as a generator during deceleration of the vehicles and collects generated electrical energy in a battery so as to use the electrical energy as a braking force. The battery has the property that the amount of input and output of the electrical energy drops dramatically when the temperature of the battery drops due to, e.g., a vehicle being left for a long time in winter time. As a result, until the temperature of the battery rises, there are less driving force assistance and amount of energy collection by the motor, lowering energy efficiency. Particularly, in the case of a lithium battery, the acceptable temperature range is extremely narrow compared to a nickel battery, etc. Therefore, it is necessary to promptly raise the battery temperature to the acceptable range in order for the improvement of energy efficiency.
Patent Document No. 1 discloses increasing the discharging current and charging current of a battery so as to raise the temperature of the battery when the temperature of the battery is low by repeating both control of increasing a motor driving force as much as a decrease in an engine driving force such that the battery discharges and control of decreasing the motor driving force as much as an increase in the engine driving force such that the battery charges.